Electrodeposition of copper



2,373,235 ELECTRODEPOSITION OF COPPER Frank Passal, Detroit, Mich, assignor to Metal & Thermit Corporation, Woodbridge Township, N. J., a corporation of New Jersey 1 N Drawing. Application June 19, 1957 Serial No. 666,784

9 Claims. (Cl. 204-52) This invention relates to electroplating of copper and more particularly to the electrodeposition of bright copper plates.

Electrodeposited copper is widely used as a decorative finish and also as an undercoat for subsequent electrodeposits such as nickel and/ or chromium. Electroplating baths acceptable to industry are desirably economic, stable, easy to maintain, and should have good plating characteristics. Alkaline-cyanide type baths are widely used because of their relatively high plating speeds, excellent throwing power, and ease of maintenance. Alkaline-cyanide electroplating baths and processes are described in Modern Electroplating, edited by A. G. Gray, pages 194-225 (1953).

I have now discovered a process for plating bright electrolytic copper from alkaline-cyanide baths containing novel additives.

It is an object of this invention to provide an efficient and economical process for electrodepositing bright and smooth copper deposits.

Another object of the invention is to provide bath compositions of the alkaline-cyanide type from which bright copper plate is electrodeposited.

Still another object of the invention is to provide compositions of matter which, when dissolved in water, yield alkaline-cyanide electrolytes suitable for the electrodeposition of bright copper electrodeposits.

Generally speaking, the invention contemplates electrodepositing copper from an alkaline-cyanide copper plating bath containing a small but efiective amount of a compound having the general formula (herein referred to as a tellurium dithiocarbamate), wherein R and R may be the same or diiferent and are selected from the class consisting of hydrogen and alkyl hydrocarbon groups having up to 6 carbon atoms in the group. R and R within the scope of the invention inelude hydrogen and alkyl groups, such as methyl, ethyl, propyl, butyl, amyl and hexyl, and the branched as well as the straight chain groups. The R and R groups may be replaced with a single alkyl cyclic compound, which may be viewed as a joinder of the R and R groups and include compounds having a total of to 7 carbon atoms in the chain. Tellurium diethyldithiocarbamate is the preferred additive.

Between about 0.001 g./l. (grams per liter) and 0.015 g./l., and preferably between about 0.006 g./l. and about 0.01 g./l. of the tellurium dithiocarbamate is included in the alkaline-cyanide copper plating baths.

Conventional alkaline-cyanide baths and process con- 2,873,235 .Patented. Feb. 10, 1959 ditions for electrod'eposition are utilized in the present invention. Typical baths and process are illustrated in the table below:

, Range CuCN g./l 30-90 KCN g./l 49-145 K CO g../l 0-112 KOH g./l 7.5-37.5 KCN (free-adjusted to and maintained) g./l 5.6-11.2 pH 13-13.8 Temp. F; -180 Cathode C. D a. s. f 10-50 Anode C. D a. s. f 10-20 The above table specifies baths and process limitations commercially preferred, and it is understood that the compositions and conditions may be varied somewhat,

.or cooperating brightening additives in conjunction with the primary tellurium dithiocarbamate. additives include relatively small amounts of salts of lead, bismuth, antimony, or zinc, e. g., lead. acetate, bismuth citrate, potassium antimony tartrate, zinc chloride,

Such auxiliary 'zinc sulfate, etc.

The alkaline-cyanide .baths utilized should preferably contain a compound selected from the class consisting of the alkali metal tartrates, citrates, gluconates, and saccharates.

Conventional wetting agents of the kind generally used in alkaline-cyanide copper electroplating baths are preferably incorporated in the baths. These include quaternary amine wetting agents such as C-decylbetaine and the ammonium hydroxide derivatives such as trimethylbenzylammonium chloride. We prefer novel and stable wetting agents of the following general-structure:

RNHCHg CH COONa (an alkyl fi-arnino propionate) or RN(CH CH COONa) (an alkyl ,B-arnino dipropionate). The above compounds, marketed under the trade name Deriphats, are used in concentrations of 0.01 to 0.1 gram per liter. They are stable in the electrolyte and even impart some brightening action. A compound of this class which has been successfully used is the sodium salt of a coconut alcohol derivative of B-arnino '15 1.

Best results are usually achieved when utilizing in the electrodeposition process a method of preventing the thin film immediately adjacent to the cathode from becoming depleted in metal (copper) ion content. This is conventionally accomplished by agitation e. g., solution pumping, cathode movement, air agitation, etc., or by diffusion elfects, e. g., current interruption, periodic current reversal etc., or by combinations thereof. Superior results have been achieved by utilizing current interruption in conjunction with cathode movement.

The following examples are illustrative of the present process and it will be understood that the invention is not limited thereto.

The potassium salts noted in the table,

propionate designated as Deriphat 3 Example N0. 1

CuCN 45 g./l. KCN 72.5 g./l. KOH 15 g./l. KcsHnoq 45 g./l. (potassium gluconate). Tellurium diethyl dithiocarbamate) 0.008 g./l. Deriphat 151 0.05 g./l.

Example N0. 2

CuCN 45 g./l. KCN 72.5 g./l. KOH 15 g./l. K C H O 45 g./l. (potassium saccharate). Tellurium dimethyl dithiocarbamate 0.008 g./l. Deriphat 1S1 0.05 g./l.

Example No. 3

CuCN 45 g./1. KCN 72.5 g./l. KOH 15 g./l. K C H O 45 g./l. (potassium saccharate). Tellurium diethyl dithiocarbamate 0.008 g./l. Pb(C H O -3H O 0.0037 g./l. (.002 g./l. Pb). Deriphat 151 0.05 g./l.

The bright copper electrodeposits obtained from the tellurium dithiocarbamate containing alkaline-cyanide baths of the present invention are obtained on such conventional basis metals as iron, steel, nickel, zinc, lead, copper, etc., and alloys'thereof. Gn certain basis metals such as iron or steel and zinc-base die-castings the basis metal is first given an initial thin flash of copper from a low efliciency cyanide copper bath.

As many embodiments of this invention may be made without departing from the spirit and scope thereof, it is to be understood that the invention includes all such modifications and variations as come within the scope of the appended claims.

Iclaim: V

. 1. ,An alkaline-cyanide bath for bright copper plating comprising copper cyanide and, as a brightening agent more than 0.001 g./l. of at least one tellurium dithiocarbamate having the general formula:

wherein R and R are selected from the class consisting of hydrogen and alkyl groups having up to six carbon atoms.

2. A bath solution according to claim 1 in which the tellurium dithiocarbamate is tellurium diethyldithiocarbamate.

3. A bath solution according to claim 1 where the tellurium dithiocarbamate is present in amounts of between about 0.001 g./l. and 0.015 g./l.

4. A bath solution according to claim 2 where the tellurium diethyldithiocarbamate is present in amounts between about 0.006 g./l. and 0.01 g./l.

5. A bath solution according to claim 1 which also contains at least one secondary brightening agent selected from the class consisting of the salts of lead, bismuth, antimony and zinc.

6. In the process of electrodepositing copper from an alkaline-cyanide copper bath comprising copper cyanide, the improvement which comprises incorporating in said bath more than 0.001 g./l. of a tellurium dithiocarbamate having the general formula:

References Cited in the file of this patent UNITED STATES PATENTS Nevers et al. Sept. 14, 1954 OTHER REFERENCES Meyer .et al.: Transactions Electrochem. Soc., vol. 73 (1938), pages 377-413.

Serial No. 351,241, Weiner (A. P. (3.) published May 18, 1943. 

1. AN ALKALINE-CYANIDE BATH FOR BRIGHT COPPER PLATING COMPRISING COPPER CYANIDE AND, AS A BRIGHTENING AGENT MORE THAN 0.001$ OF AT LEAST ONE TELLURIUM DITHIOCARBAMATE HAVING THE GENERAL FORMULA: 